In recent years, there have been concerns such as global warming and aerial pollution caused by carbon dioxide (CO2), nitrogen oxide (NOX), and suspended particulate matter (PM). For this reason, instead of an existing gasoline internal-combustion engine vehicle, a fuel cell vehicle (FCV) which is driven by using electric energy based on an oxidization reaction between hydrogen and oxygen in a fuel cell mounted on the vehicle has been gaining attention.
The fuel cell vehicle does not discharge any toxic matter in addition to the above-described carbon dioxide and the like. Further, the fuel cell vehicle has energy efficiency better than that of the gasoline internal-combustion engine vehicle. Likewise, the fuel cell vehicle has various advantages that may not be obtained from the gasoline internal-combustion engine vehicle.
Incidentally, the fuel cell vehicle may be largely classified into a type in which hydrogen is charged from a hydrogen station to the vehicle and a type in which a fuel other than hydrogen is charged to the vehicle and hydrogen is produced in a vehicle installed reforming unit. However, the former type has more advantages from the effect of a reduction of carbon dioxide (CO2). Accordingly, there is a need to more actively study and develop the fuel cell vehicle and the hydrogen station that charge hydrogen to the fuel cell vehicle.
In a case of the fuel cell vehicle of the type in which hydrogen (hydrogen gas) is charged from the hydrogen station to the vehicle, compressed hydrogen is charged to a hydrogen tank mounted on the vehicle.
Incidentally, in a case where a gas is expanded while a difference in pressure thereof is maintained when a high-pressure gas of a supply source is transferred (that is, expanded) to a low-pressure state of a supply target, a change in temperature occurs in the gas due to the Joule-Thompson effect.
A change in temperature caused by the Joule-Thompson effect depends on the initial temperature of the gas. When the initial temperature is equal to or lower than the inversion temperature, the temperature of the gas decreases. Then, when the initial temperature is higher than the inversion temperature, the temperature of the gas increases. Here, the inversion temperature of the hydrogen is about 215 K (−58.15° C.). Since this inversion temperature is fairly lower than those of the other gases, when the hydrogen is generally charged to the hydrogen tank of the fuel cell vehicle or the like, an abrupt increase in temperature occurs in the charged hydrogen.
Accordingly, in the hydrogen station, there is a need to suppress an increase in the internal temperature of the hydrogen tank caused by an abrupt increase in temperature of the hydrogen when the hydrogen is charged to the hydrogen tank. Thus, various proposals have been suggested. For example, Patent Document 1 discloses a method of quickly charging hydrogen to a hydrogen tank (and a hydrogen station realizing the quick hydrogen charging method) including the steps of connecting a hydrogen supply source to a hydrogen tank and increasing a hydrogen charging speed in response to a pressure inside the hydrogen tank by a charging speed changing unit provided in the course of a passage connecting the hydrogen supply source to the hydrogen tank.
As described above, in the hydrogen station, there is a need to suppress an increase in the internal temperature of the hydrogen tank caused by an abrupt increase in temperature of the hydrogen when the hydrogen is charged to the hydrogen tank. For this reason, various proposals have been suggested, but more proposals have been demanded from the viewpoint of enrichment of technologies.
Incidentally, the hydrogen station generally includes a compressor which compresses the hydrogen to be supplied to the fuel cell vehicle or the like.
In order to charge a large amount of hydrogen to the hydrogen tank of the supply target, the compressor needs to have an ability of increasing the pressure of the hydrogen to a very high pressure of 100 MPa. For this reason, as the compressor dedicated for the hydrogen station, adoption of a so-called reciprocating compressor has been examined. Furthermore, as the reciprocating compressor, a diaphragm type compressor, a piston type compressor, a plunger type compressor, an ionic compressor, and the like are known.
In the reciprocating compressor, a “suction valve unloading method” and a “clearance pocket method” are adopted in many cases as a means for adjusting the amount of a fluid to be supplied. The suction valve unloading method is a method of adjusting a flow rate of a gas in a manner such that a suction valve plate of a cylinder is pushed to be opened and an initially suctioned gas is made to reversely flow to a suction side so as not to undergo a compressing process. Meanwhile, the clearance pocket method is a method of adjusting a flow rate of a gas in a manner such that a clearance pocket attached to a cylinder head or the like is opened and closed so as to change a size of a gap (clearance).
However, since the flow rate is gradually adjusted in any method of the “suction valve unloading method” and the “clearance pocket method”, it is difficult to perform a uniform temperature control in the hydrogen station.
Furthermore, as the “suction valve unloading method”, a method is proposed which continuously adjusts the capacity in the range of about 20 to 100% by combining a hydraulic control with a suction valve unloading mechanism, but this method is not practical in that a facility greatly increases in size.